Enhancing Security in an IS-IS Network

This module describes processes that you can follow to enhance network security when you use Intermediate System-to-Intermediate System (IS-IS) in your network. You can set passwords, prevent unauthorized routers from forming adjacencies with routers in your IS-IS network, and use the IS-IS HMAC-MD5 Authentication and Enhanced Clear Text Authentication feature.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see
Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Prerequisites for Enhancing Security in an IS-IS Network

Before performing the tasks in this module, you should be familiar with the concepts described in the "Integrated IS-IS Routing Protocol Overview" and "Configuring a Basic IS-IS Network" modules.

It is assumed you already have IS-IS running on your network.

Information About Enhancing Security in an IS-IS Network

Importance of Preventing Unauthorized Information from Entering an IS-IS Network

It is recommended that you configure the security features described in this module in order to prevent unauthorized routing messages from being placed into the network routing domain. You can set an authentication password for each interface, as well as set an area password for each IS-IS area to prevent unauthorized devices from injecting false routing information into the link-state database, or you can configure a type of IS-IS authentication--either IS-IS HMAC-MD5 or enhanced clear text authentication.

The following sections describe configuration tasks for IS-IS authentication. Two types of authentication are supported: IS-IS HMAC-MD5 and clear text. The task you perform depends on whether you are introducing authentication or migrating from an existing authentication scheme.

Before you can configure authentication, you must make the following decisions:

Whether to configure authentication for the IS-IS instance and/or for individual IS-IS interfaces (both tasks are included in this section).

At what level(s) authentication is to be used.

What type of authentication (IS-IS HMAC-MD5 or clear text) is to be used.

IS-IS Authentication Functionality

New style IS-IS authentication (IS-IS HMAC-MD5 and clear text) provides a number of advantages over the old style password configuration commands that were described in the previous sections, "Setting an Authentication Password for each Interface" and "Setting a Password at Level 1".

Passwords are encrypted when the software configuration is displayed.

Passwords are easier to manage and change.

Passwords can be rolled over to new passwords without disrupting network operations.

Non-disruptive authentication transitions are supported by allowing configuration which allowed the router to accept PDUs without authentication or with stale authentication information, yet send PDUs with current authentication. Such transitions are useful when you are migrating from no authentication to some type of authentication, when you are changing authentication type, and when you are changing keys.

IS-IS has five PDU types: link state PDU (LSP), LAN Hello, Point-to-Point Hello, complete sequence number PDU (CSNP), and partial sequence number PDU (PSNP). IS-IS HMAC-MD5 authentication or clear text password authentication can be applied to all five PDU types. The authentication can be enabled on different IS-IS levels independently. The interface-related PDUs (LAN Hello, Point-to-Point Hello, CSNP, and PSNP) can be enabled with authentication on different interfaces, with different levels and different passwords.

Either authentication mode or old password mode may be configured on a given scope (IS-IS instance or interface) and level--bit not both. However, different modes may be configured for different modes mat be configured for different scopes or levels. If mixed modes are intended, different keys should be used for different modes in order not to compromise the encrypted password in the PDUs.

Benefits of IS-IS Clear Text Authentication

IS-IS clear text (plain text) authentication provides the same functionality as is provided by using the area-password or domain-password command. However, use of clear text authentication takes advantage of the more flexible key management capabilities described above.

Benefits of IS-IS HMAC-MD5 Authentication

IS-IS now supports MD5 authentication, which is more secure than clear text authentication. IS-IS HMAC-MD5 authentication adds an HMAC-MD5 digest to each IS-IS protocol data unit (PDU). HMAC is a mechanism for message authentication codes (MACs) using cryptographic hash functions. The digest allows authentication at the IS-IS routing protocol level, which prevents unauthorized routing messages from being injected into the network routing domain.

MD5 authentication or clear text authentication can be enabled on Level 1 or Level 2 independently.

Passwords can be rolled over to new passwords without disrupting routing messages.

For the purpose of network transition, you can configure the networking device to accept PDUs without authentication or with wrong authentication information, yet send PDUs with authentication. Such transition might be because you are migrating from no authentication to some type of authentication, you are changing authentication type, or you are changing keys.

Before you migrate from using one type of security authentication to another, all routers must be loaded with the new image that supports the new authentication type. The routers will continue to use the original authentication method until all routers have been loaded with the new image that supports the new authentication method, and all routers have been configured to use the new authentication method. Once all routers are loaded with the required image, you must follow the configuration steps for the desired new authentication method as described in the previous Configuring HMAC-MD5 or Clear Text Authentication for the IS-IS Instance. You also must decide whether to configure authentication for the IS-IS area or for individual IS-IS interfaces. Both tasks are included in the referenced section.

Note

To achieve a smooth transition from one authentication method to another, allowing for continuous authentication of IS-IS PDUs, perform the task steps in the order shown, which requires moving from router to router doing certain steps before all the steps are performed on any one router.

Migration from Old Clear Text Authentication to HMAC-MD5 Authentication

When you configure MD5 authentication, the area-password and domain-password command settings will be overridden automatically with the new authentication commands. When you configure MD5 authentication, the isispassword command setting will be overridden automatically with the new authentication commands.

Migration from Old Clear Text Authentication to the New Clear Text Authentication

The benefits of migrating from the old method of clear text authentication to the new method of clear text authentication are as follows:

Passwords are easier to change and maintain.

Passwords can be encrypted when the system configuration is being displayed (if you use key management).

Setting a Password at Level 2

This password is exchanged as plain text, and, thus, this feature provides only limited security.

SUMMARY STEPS

1.enable

2.configureterminal

3.routerisis[area-tag]

4.domain-passwordpassword [authenticatesnp {validate |
send-only}]

5.end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

routerisis[area-tag]

Example:

Device(config)# router isis salesarea

Enables IS-IS as an IP routing protocol and assigns a tag to a process, if required.

Enters router configuration mode.

Step 4

domain-passwordpassword [authenticatesnp {validate |
send-only}]

Example:

Device(config-router)# domain-password company2

Configures the IS-IS routing domain authentication password.

Note

If you do not specify the
authenticatesnp keyword along with either thevalidate or
send-only keyword, the IS-IS routing protocol does not insert the password into SNPs.

Note

Using the
domain-password command on all devices in an area will prevent unauthorized devices from injecting false routing information into the link-state database.

Note

This password is inserted in Level 2 PDU link-state PDUs (LSPs), complete sequence number PDUs (CSNPs), and partial sequence number PDUs (PSNPs). If you specify the
authenticatesnp keyword along with either the
validate or
send-only keyword, the IS-IS routing protocol will insert the password into sequence number PDUs (SNPs).

Configuring HMAC-MD5 Authentication or Clear Text Authentication for the First Time

Configuring HMAC-MD5 or Clear Text Authentication for the IS-IS Instance

Before You Begin

In order to use HMAC-MD5 or clear text authentication with encrypted keys, the Integrated IS-IS routing protocol must be configured.

SUMMARY STEPS

1.enable

2.configureterminal

3.keychainname-of-chain

4.keykey-id

5.key-stringtext

6.exit

7.exit

8.routerisis [area-tag]

9.authenticationsend-only [level-1 |
level-2]

10. Repeat Steps 1 through 9 on each device that will communicate.

11.authenticationmode{md5 |
text}[level-1 |
level-2]

12.authenticationkey-chainname-of-chain[level-1 |
level-2]

13. Repeat Steps 11 and 12 on each router that will communicate.

14.noauthenticationsend-only

15. Repeat Step 14 on each device that will communicate.

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

keychainname-of-chain

Example:

Device(config)# key chain remote3754

Enables authentication for routing protocols and identifies a group of authentication keys.

Step 4

keykey-id

Example:

Device(config-keychain)# key 100

Identifies an authentication key on a key chain.

The
key-id argument must be a number.

Step 5

key-stringtext

Example:

Device(config-keychain-key)# key-string mno172

Specifies the authentication string for a key.

The
text argument can be 1 to 80 uppercase or lowercase alphanumeric characters; the first character cannot be a number.

Step 6

exit

Example:

Device(config-keychain-key)# exit

Returns to keychain configuration mode.

Step 7

exit

Example:

Device(config-keychain)# exit

Returns to global configuration mode.

Step 8

routerisis [area-tag]

Example:

Device(config)# router isis 1

Enables IS-IS as an IP routing protocol and assigns a tag to a process, if required.

Enters router configuration mode.

Step 9

authenticationsend-only [level-1 |
level-2]

Example:

Device(config-router)# authentication send-only

Specifies for the IS-IS instance that MD5 authentication is performed only on IS-IS PDUs being sent (not received).

Step 10

Repeat Steps 1 through 9 on each device that will communicate.

Use the same key string on each device.

Step 11

authenticationmode{md5 |
text}[level-1 |
level-2]

Example:

Device(config-router)# authentication mode md5

Specifies the type of authentication used in IS-IS PDUs for the IS-IS instance.

Specify
md5 for MD5 authentication.

Specify
text for clear text authentication.

Step 12

authenticationkey-chainname-of-chain[level-1 |
level-2]

Example:

Device(config-router)# authentication key-chain remote3754

Enables MD5 authentication for the IS-IS instance.

Step 13

Repeat Steps 11 and 12 on each router that will communicate.

--

Step 14

noauthenticationsend-only

Example:

Device(config-router)# no authentication send-only

Specifies for the IS-IS instance that MD5 authentication is performed on IS-IS PDUs being sent and received.

In Step 9 you enable authentication to be performed only for IS-IS PDUs that are being sent. In Step 14 you enter the
noauthenticationsend-only command so that the authentication is now performed on PDUs sent and received.

Step 15

Repeat Step 14 on each device that will communicate.

--

Configuring HMAC-MD5 or Clear Text Authentication for an IS-IS Interface

SUMMARY STEPS

1.enable

2.configureterminal

3.keychainname-of-chain

4.keykey-id

5.key-stringtext

6.exit

7.exit

8.interfacetypenumber

9.isisauthenticationsend-only [level-1 |
level-2]

10. Repeat Steps 1 through 9 on each device that will communicate.

11.isisauthenticationmode{md5 |
text}[level-1 |
level-2]

12.isisauthenticationkey-chainname-of-chain[level-1 |
level-2]

13. Repeat Steps 11 and 12 on each router that will communicate.

14.noisisauthenticationsend-only

15. Repeat Step 14 on each device that will communicate.

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

keychainname-of-chain

Example:

Device(config)# key chain multistate87723

Enables authentication for routing protocols and identifies a group of authentication keys.

Step 4

keykey-id

Example:

Device(config-keychain)# key 201

Identifies an authentication key on a key chain.

The
key-id argument must be a number.

Step 5

key-stringtext

Example:

Device(config-keychain-key)# key-string idaho

Specifies the authentication string for a key.

The
text argument can be 1 to 80 uppercase or lowercase alphanumeric characters; the first character cannot be a number.

Step 6

exit

Example:

Device(config-keychain-key)# exit

Returns to keychain configuration mode.

Step 7

exit

Example:

Device(config-keychain)# exit

Returns to global configuration mode.

Step 8

interfacetypenumber

Example:

Device(config)# interface gigabitethernet 0/0/0

Configures an interface.

Step 9

isisauthenticationsend-only [level-1 |
level-2]

Example:

Device(config-if)# isis authentication send-only

Specifies that authentication is performed only on PDUs being sent (not received) on a specified IS-IS interface.

Step 10

Repeat Steps 1 through 9 on each device that will communicate.

Use the same key string on each device.

Step 11

isisauthenticationmode{md5 |
text}[level-1 |
level-2]

Example:

Router(config-if)# isis authentication mode md5

Specifies the type of authentication used for an IS-IS interface.

Specify
md5 for MD5 authentication.

Specify
text for clear text authentication.

Step 12

isisauthenticationkey-chainname-of-chain[level-1 |
level-2]

Example:

Device(config-if)# isis authentication key-chain multistate87723

Enables MD5 authentication for an IS-IS interface.

Step 13

Repeat Steps 11 and 12 on each router that will communicate.

--

Step 14

noisisauthenticationsend-only

Example:

Device(config-if)# no isis authentication send-only

Specifies that authentication is performed on PDUs being sent and received on a specified IS-IS interface.

Step 15

Repeat Step 14 on each device that will communicate.

--

Migrating to a New Authentication Type

SUMMARY STEPS

1. Load all devices with the image required to support the new, desired authentication method.

MIBs

Technical Assistance

Description

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Feature Information for
Enhancing Security in an IS-IS Network

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

The IS-IS
HMAC-MD5 authentication feature adds an HMAC-MD5 digest to each Intermediate
System-to-Intermediate System (IS-IS) protocol data unit (PDU). The digest
allows authentication at the IS-IS routing protocol level, which prevents
unauthorized routing messages from being injected into the network routing
domain. IS-IS clear text (plain text) authentication is enhanced so that
passwords are encrypted when the software configuration is displayed and
passwords are easier to manage and change.

This
feature was introduced on the Cisco ASR 1000 Series Aggregation Services
Routers.